The Seadogs, managed by former Blade Russell Slade reached Fourth round of the FA Cup, only to lose 1-0 at home to Chelsea.
Cryan, who has played twice for the Blades this season spent three months on loan at the McCain Stadium, playing 10 games and scoring a goal against Gravesend & Northfleet.
Thierry Henry body double, Sestanovich also spent three months on loan, both were involved the the Cup wins over Doncaster Rovers, Port Vale and Southend United.
The Midfielder, who was a £10,000 buy from Hampton & Richmond late last season scored 3 times in 13 games for the Seadogs. All the goals came in consecutive matches against Port Vale, Farnborough and Northwich.